Preparation Of Tetraphenylethylene-based And Phenothiazine-based Fluorescent Polymers And Their Application In Biological Imaging

Aggregation-induced emission（AIE）effect refers to the phenomenon that certain molecules do not emit fluorescence or emit very weak fluorescence in good solvent,but emit fluorescence or emit stronger fluorescence in the aggregation state.The discovery of the AIE phenomenon has solved the problem of the limitation of the practical application of fluorescent organic materials caused by the Aggregation-caused quenching（ACQ）effect to a certain extent,and is of great significance to the design,synthesis and application of new fluorescent materials.Since then,more and more researchers have focused on the development of new AIE materials,and these materials are widely used in ion detection,bioimaging,biomolecule detection,medical diagnosis and treatment and other fields.Due to the excellent properties of the polymer,such as the designable molecular structure,and stable performance,the fluorescent polymer nanoparticles（FPNs）with AIE effect have suddenly emerged,becoming the focus and hot spot in the field of fluorescent organic materials.In this paper,tetraphenylethene and phenothiazine are used as the basic framework to design and synthesize a variety of new polymerizable AIE molecules.And the corresponding AIE amphiphilic fluorescent polymer was synthesized by RAFT polymerization between AIE molecule and PEGMA.In aqueous solution,these amphiphilic fluorescent polymers are easy to self-assemble into FPNs.At the same time,the application potential of these FPNs in cell imaging was explored.The specific research contents are as follows:（1）Based on tetraphenylethene,a novel AIE-active dye tetraphenylethylene diphenylaldehyde（TPDA）with terminal aldehyde group was synthesized.Subsequently,the corresponding novel polymers PEG-TPD were obtained through the one-pot combination of Hantzsch reaction and RAFT polymerization.The molecular weights（Mn）of the polymers PEG-TPD1 and PEG-TPD2 were respectively 52000 g/mol and 28000 g/mol,and their molar fractions of TPDA were respectively about 9.5%and 14.3%.In aqueous solution,these amphiphilic PEG-TPD polymers tended to self-assemble into corresponding FPNs.The diameter of PEG-TPD2 FPNs ranged from 200 to 300 nm,and their maximum fluorescence emission wavelength is 509 nm.The PEG-TPD FPNs have sianificant advantages such as good fluorescence intensity and good biocompatibility which have great potential in the field of bioimaging.（2）Based on tetraphenylethene,a novel acrylate AIE-active dye of TPMA was successfully synthesized and belongs to the monoclinic crystal system and P21/c space qroup,and the obtained TPMA dve exhibits multi-stimuli-responsivity and a two-photon fluorescent switch with excellent reversibility in the solid state.Subsequently,the corresponding fluorescent polymers of PEG-TM were successfully fabricated with a molecular weight of about 25000 g/mol and narrow PDI.From 1H NMR analysis,when the feeding ratio of TPMA increased to 32.2%from 19.2%,the molar fraction of TPMA in PEG-TM polymers accordinaly increased to 32.8%from 19.5%.In water solution.the as-prepared PEG-TM1 polymers would self-assemble into FPNs with 150-250 nm diameters,and their maximum emission wavelenath presented at 518 nm with obvious AlE phenomena.Moreover,the as-synthesized PEG-TM polymers have prospective application in biological imaging due to their good fluorescence,high water solubility and excellent biocompatibility.（3）Based on tetraphenylethene,a new fluorescent monomer（R）-THM with chirality and AIE effect was first synthesized and its specific optical rotation[α]_D^25℃ was-9.67°.Subsequently,chiral fluorescent polymers PEG-（R）-THM1 and PEG-（R）-THM2 were synthesized,and their molecular weights were about 20000 g/mol.The the actual（R）-THM molar fractions in the chiral polymer PEG-（R）-THMl and PEG-（R）-THM2 were about 22.3%and 30.2%.And the[α]_D^25℃ of chiral polymer PEG-（R）-THM2 was-3.74°.The polymers PEG-（R）-THM self-assembled into nanoparticle with a size of 100-150 nm in aqueous solution.The maximum emission wavelength of PEG-（R）-THM1 FPNs in water presented at 495 nm,with obvious AIE effect.Meanwhile,the PEG-（R）-THM FPNs had good biological compatibility and good cell imaging effect,which showed the great potential of polymers PEG-（R）-THM in bioimaging.（4）Based on phenothiazine,a new fluorescent monomer（R）-PVHMA with chirality and AIE effect was first synthesized.The[α]_D^25℃ of the monomer（R）-PVHMA was-6.39°.Subsequently,chiral fluorescent polymers PEG-（R）-PVH1 and PEG-（R）-PVH2 were synthesized,and the actual（R）-PVHMA molar fraction in the chiral polymers were respectively about 18.1%and 25.7%.And the[α]_D^25℃of chiral polymer PEG-（R）-PVH2 was-2.96°.The amphiphilic polymer PEG-（R）-PVH self-assembled into nanoparticles in aqueous solution with about 100 nm in diameter.The maximum fluorescence emission wavelength of PEG-（R）-PVH1 FPNs in water is 565 nm.The investigation of cytotoxicity and cell uptake shows that PEG-（R）-PVH FPNs have good biocompatibility and good cell imaging effect,and have great potential in bioimaging.